Prior Art
Cutting inserts for chip removing machining become heated under the machining operations which causes the heat to quickly spread through the cutting insert. The cutting insert, which generally consists of cemented carbide, therefore reaches, in a very short time, a range of temperatures within which the resistance to plastic deformation of the cutting insert material decreases. When large cutting forces act on the cutting insert this phenomenon entails a risk that the cutting insert will be subject to plastic deformation in particular in the proximity of the cutting edge, whereby insert breakage can result. In order to diminish the risk of plastic deformation an efficient system for the cooling of the cutting insert is required such that the working temperature of the insert can be regulated within desired limits. Generally, the cutting insert and the surrounding so-called cutting zone, are cooled by a cooling medium in fluid form which is led from outside to flow towards the area where the heat is generated. Previously, such a supply of cooling medium has been generally arranged from above and been directed downwardly towards the cutting insert and the chips which are broken against the chip breaking upper side of the cutting insert. This method of supply, however, results in only a very limited amount of the cooling medium having any practical effect on the cutting insert. That is, because of the presence of the chips, the cutting edge is only exposed to the cooling medium to a very limited degree.
Another means of supplying cooling medium in fluid form is to steer the medium in a direction between the chip breaking surface of the cutting insert and the chip itself. However, when the cooling liquid is applied at normal pressures this procedure does not result in any significant improvement in cooling effect compared to the aforementioned methods because the cooling liquid does not reach that part of the cutting insert which is hottest and which is exposed to the greatest mechanical load. Thus, a clear risk exists of the cutting insert becoming plastic because of excessively high temperature. The effect of the cooling can certainly be increased considerably by increasing the pressure of the cooling liquid to very high levels, e.g., 250-300 Mpa, but the equipment required to raise the cooling liquid pressure to this level is very complicated and expensive. Working with extremely high fluid pressure is furthermore, in practice, associated with appreciable safety risks.
In order to overcome the problem indicated above it has been proposed more recently that the cutting insert itself be cooled from within, with the prime aim of holding the temperature in the cutting insert at such a low level that the risk of plastic deformation is to all intents and purposes eliminated. Several different solutions as to the problem of how to provide internal cooling of cutting inserts are to be found in the patent literature for this area. Thus Swedish Patent 467 649 describes a cutting insert which is composed of two identical, partial bodies which are sintered together in such a way as to form internal, open channels through which the cooling medium can flow. Swedish Patent No. 429 934 describes a cutting insert with a transverse hole through which cooling medium can pass from an underlying shim in the direction towards a separate cover plate on the upper side of the cutting insert in order to be finally directed towards the cutting edge of the insert. French Patent 2,244,590 describes a cutting insert with a transverse channel for the cooling medium which extends from the underside of the cutting insert to the upper side where it discharges in the immediate vicinity of the cutting insert's cutting edge. European Publication 0 534 450 describes a cutting insert for parting, the insert having an open groove disposed in the clearance surface of the cutting insert for the transport of cooling medium from a channel in the corresponding tool holder in the direction of the cutting insert edge. U.S. Pat. No. 5,237,894 describes a cutting insert with a transverse, open channel for cooling liquid which terminates in an opening on the upper side of the cutting insert.
Common to all the solutions to the problem indicated above, which are based on transverse or open channels or grooves for feeding the cooling medium, is that the channels weaken the cutting insert in the cutting edge area and there is a risk that the channels will be blocked by the hot material of the chip which sticks to the insert surface. Furthermore, the existence of the channels or grooves limits the possibilities to design the cutting insert with an optimal chip breaker geometry.
It should also be mentioned that Swedish Document No. 377 290 describes a cutting insert with an internal cavity in which cooling medium can circulate. However, this cavity weakens the cutting insert to such a large degree that its use is not practical when exposed to typical cutting forces.